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Arterial supply to brain:Anterior cerebral artery (ACA), segments
The anterior cerebral artery along with the middle cerebral artery, forms at the termination of the internal carotid artery. It branches off at the anterior perforated substance and passes forward above the optic nerve and then arches antro-medially to pass anterior to genu of the corpus callosus as the callosomarginal artery. It supplies the orbital surface of the frontal lobe and the medial aspect of the cerebral hemispheres above the corpus callosum as far back as the parietal lobe. Segments: The ACA is divided into three segments: * A1 (horizontal): origin from the ICA to the anterior communicating artery (ACOM) ~14 mm in length. Courses medially above optic chiasm and joined by anterior communicating artery. * A2 (vertical): from ACOM to the origin of the callosomarginal artery. Courses superiorly in the interhemispheric fissure an around the corpus callosum genu. * A3 (callosal): pericallosal segment distal to the origin of the callosomarginal artery. Courses posteriorly under free margin of falx cerebri above CC, giving off cortical branches. Branches off the ACA There are two main branching patterns of the ACA. Either A2 continues as the callosomarginal artery (lies in the cingulate sulcus), which gives off the terminal branches, and gives the pericallosal artery branch OR A2 continues as pericallosal, giving terminal branches an the callosomarginal is absent. * A1: ** medial lenticulostriate artery: course superiorly through anterior perforated substance *** recurrent artery of Heubner: curves back laterally above A1 to enter anterior perforated substance to basal ganglion and anterior limb of internal capsule. ** anterior communicating artery * A2 ' ** orbitofrontal artery: supply inferior part of frontal lobe ** frontopolar artery: extends anteriorly to frontal pole * '''A3 ' ** pericallosal artery: courses posterosuperiorly above corpus callosum, below cingulate gyrus. Arise near the genu of CC. ** callosomarginal artery arise near the genu of CC, and pass up the superior border of the frontoparietal region ** callososeptal artery Terminal (cortical) branches '''Orbital branches from the A2: (orbitofrontal and frontopolar arteries) supply over the orbital surface of the frontal lobe: * olfactory cortex * gyrus rectus * medial orbital gyrus Frontal branches supply: * corpus callosum (with the exception of the splenium) via pericallosal artery. * cingulate gyrus * medial frontal gyrus * paracentral lobule (as the branches reach over the vertex to supply a stip of cortex on the surface, they are responsible for supply to the lower limbs) Parietal branches supply: * precuneus Central branches: multiple small branches given off proximally (A1, ACOM, proximal A2) supply: * anterior perforated substance * lamina terminalis * rostrum of the corpus callosum * septum pellucidum * anterior part of the putamen * head of the caudate nucleus * anteromedial part of the anterior limb of the internal capsule The latter two (head of caudate and adjacent part of the internal capsule) are supplied by the recurrent artery of Heubner and associated smaller perforating branches. It has its origin near the A1-ACOM-A2 junction and can arise from all three, although usually it is from the A2. It curves back on itself and is at risk from ACOM aneurysm clipping. Normal variants * ACA fenestration with a reported incidence of 0-4% of A1 segment fenestration * azygos ACA: ACA territories supplied by a single A2 trunk; incidence of ~2% (range 0.2-4.0%) * ACA trifurcation: three A2 segments; incidence of ~7.5% (range 2-13%) * Bihemispheric ACA: hypoplastic A2 segment with contralateral A2 segment dominance supplying both ACA territories; incidence of ~4.5% (range 2-7%) * A1 segment absence/hypoplasia, contralateral A1 segment dominance and supply to ipsilateral A2 segment by a large anterior communicating artery; 10 % of individuals demonstrate hypoplasia of A1 segment using a diameter 1.5 mm or smaller * Asymmetry of A1 segment which is associated with ACA aneurysm * Persistent primitive olfactory artery